You can install 32 bit software on 64 bit architecture JUST LIKE installing 32 on 32 or 64 on 64.
Your question isn't about installing 32 on 64, its about linking a 32 bit object to a 64 bit program. The answer is - you don't.
You've got 2 choices;
nspluginwrapper - think of that as a translator, specifically for browser plugins.
Install 32bit firefox - this is a better idea.
To install 32bit firefox;
yum -y install firefox-32
Note that this can COEXIST with 64bit firefox. You just can't run them both at the same time. You then install your 32bit objects in /usr/lib/mozilla/plugins/, and run firefox-32 when you want to use those plugins.